FID differs from other generative readers [1]}, [2]} in that it processes passages independently in the encoder but jointly in the decoder. As pointed out by [3]}, the computational cost of FID grows linearly with the number of passages, instead of quadratically since the encoder of FID only performs self-attention over one context at a time. On the other hand, conditioning on all passage encodings jointly allows the decoder to effectively aggregate evidence from multiple passages.
